1. Field of the Invention
The present invention relates to a stabilizer apparatus for a vehicle which can change the torsional stiffness of a stabilizer.
2. Description of the Related Art
Japanese Kohyo (PCT) Patent Publication No. 2002-518245 discloses a conventional vehicle stabilizer apparatus including a motor-driven actuator which comprises an electric motor and a speed reduction mechanism and is disposed between two sections of a divided stabilizer so as to rotate one section of the stabilizer in relation to the other section thereof about an axis of the stabilizer. In the stabilizer apparatus, a target current which must flow through the electric motor so as to suppress a roll of the vehicle is determined, and the current flowing through the electric motor is increased or decreased such that the determined target current flows through the electric motor.
In the conventional apparatus, the output torque of the speed reduction mechanism increases at a certain gradient (regular efficiency) with the increasing current flowing through the electric motor. However, when the current flowing through the electric motor is gradually reduced in this state, the output torque of the speed reduction mechanism does not decrease immediately to follow the decreasing current, because the electric motor remains in a stopped state (locked state) because of friction of the speed reduction mechanism or the like, whereby the output torque is maintained at the increased level. After that, when the current flowing through the electric motor decreases to a certain level, because of restoration force generated by the stabilizer, the output torque starts to decrease at a certain gradient (reverse efficiency) to follow the decreasing current flowing through the electric motor. As described above, a delay time is present between a point in time when the output torque has reached a certain level and a point in time when the output torque starts to decrease to follow the decreasing current flowing through the electric motor. Therefore, the output torque of the speed reduction mechanism fails to follow the current flowing through the electric motor, with a resultant deterioration in responsiveness.